This invention pertains to inkjet inks, more specifically to pigmented inkjet inks containing crosslinked polyurethane dispersoid binders, which are particularly suitable for printing on paper and other media substrates.
Inkjet recording is a printing method wherein droplets of ink are ejected through fine nozzles to form letters or figures on the surface of recording media. Inks used in such recording are subject to rigorous demands including, for example, good dispersion stability, ejection stability, and good fixation to media.
Both dyes and pigments have been used as colorants for inkjet inks. While dyes typically offer superior color properties compared to pigments, they tend to fade quickly and are more prone to rub off. Inks comprising pigments dispersed in aqueous media are advantageously superior to inks using water-soluble dyes in water-fastness and light-fastness of printed images. Additives to the ink formulation are often required to achieve water-fastness.
Pigments suitable for aqueous inkjet inks are in general well known in the art. Traditionally, pigments are stabilized by dispersing agents, such as polymeric dispersants or surfactants, to produce a stable dispersion of the pigment in the vehicle. Other additives to the ink modify the ink to match the needs for the target printed system, which includes the media.
U.S. Pat. No. 6,034,154 discloses polymer fine particles, each polymer fine particle containing a colorant. One of the candidate polymers making up the polymer portion of the fine particle is described as a crosslinked polyurethane.
U.S. Pat. No. 6,136,890 describes pigmented inks that contain pigments and polyurethane dispersants that stabilize the pigments. The pigment is dispersed by the polyurethane via dispersing techniques used to achieve a stabile pigment dispersion.
U.S. Pat. No. 6,713,531 describes a water-based pigmented ink for use in inkjet printing (on paper and transparency media). The ink consists of a pigment and a latex, of which un-crosslinked polyurethanes are listed as candidate latexes.
WO03/029318 describes polyurethane block copolymers as dispersants for inks. These polyurethanes are crosslinked prior to inversion (addition of water to produce the polyurethane dispersion) not during or after inversion. There is also crosslinking derived from the added melamine crosslinker that is only effective at high temperatures and/or acidic conditions that occur at the time of the textile treatments after printing.
U.S. Pat. No. 6,063,834 describes an ink composition that can contain a polyurethane having chemical components that would make it hydrophobic and likely not dispersible in water.
The disclosures of all of the above-identified publications are incorporated by reference for all purposes as if fully set forth.
A disadvantage of inkjet printing, in particular inkjet printing with pigmented ink, is inkjet printed paper can lack durability that is required for the printed paper. Waterfastness is of the printed image still needs improvement.
Still, there is need in the art for improved durability of inkjet images, especially on paper, and especially in cases where the colorant is pigment.